Various electro-optical systems have been developed for reading optical indicia, such as barcodes. A barcode is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Some of the more popular barcode symbologies include: Uniform Product Code (UPC), typically used in retail stores sales; Code 39, primarily used in inventory tracking; and Postnet, which is used for encoding zip codes for U.S. Mail. Systems that read and decode barcodes employing CCD or CMOS-based imaging systems are typically referred to as imaging-based barcode readers or barcode scanners.
Imaging systems include CCD arrays, CMOS arrays, or other imaging pixel arrays having a plurality of photosensitive elements or pixels. Light reflected from a target image, e.g., a target barcode is focused through a lens of the imaging system onto the pixel array. An analog-to-digital converter digitizes output signals from the pixels of the pixel array. Decoding circuitry of the imaging system processes the digitized signals and attempts to decode the imaged barcode.
It is desirable for a portable barcode scanner to have a streamline shape for ease in operation. As such, a portable or hand held barcode scanners lack physical aiming devices or sites. Instead, an aiming pattern is projected onto the desired barcode during the scanning process. This typically involves an operator engaging a trigger located on the scanner, which enables the aiming pattern to be projected while simultaneously initiating the decoding process of the image or barcode to be scanned.
The aiming pattern may be turned off when an imaging system of the scanner captures the images required for decoding, and the aiming pattern is completely inactive or disabled when the scanner successfully decodes an image. The relatively short time to turn off the aiming pattern (usually approximately 10 ms) to capture the images produces a misconception that the aiming pattern is active for the entire duration of the decode session.
The lack of a physical aiming device, and the inability of the projected aiming pattern being activated ahead of the pull-trigger create several problems during operation of portable barcode scanners. For example, if the aiming pattern was found to be aimed at the wrong barcode, it becomes too late for initiating a corrective measure, especially in scanners where the images are taken at substantially the same time as activation of the aiming pattern. This problem is exacerbated by the fact that barcodes are commonly arranged in a “pick-list” configuration, where a sheet is populated with several barcodes arranged in an array.
One attempt to alleviate the described problem has been designing a scanner with an imager capable of detecting motion. This type of system relies on the principle that the user is attempting to scan items with the portable scanner when motion was detected between images, thus activating the aiming pattern without engagement of the scanner trigger. Once the operator verifies that the scanner was targeted at the proper barcode, the trigger was then activated to scan the barcode. Several problems however, resulted from the aforementioned approach. One problem with this approach is the detection of motion that was not in the sense real or intended to initiate the scanning process, and thereby, falsely enabled the aiming pattern. This false motion problem frequently occurred when the portable scanner was positioned in a stand while not in use continued to detect objects that passed in front of the imaging system. In addition, improper scans frequently occurred whenever there was a change in lighting, since the imagining system would falsely sense that motion was occurring.
Another type of error may arise when an operator fails to move the scanner within the allotted time, thus causing a false decode to be registered. Although the wait time for confirming a correctly aimed barcode can be customized for each operator, such that it is not too fast for the operator to move in time when needed, nor too slow when no motion was needed after a trigger-pull, such customization is often not practical. For example, in many point of sale situations more than one operator gets to use a scanner during the course of a business day.
What is needed is a high-speed and efficient manner of scanning varying indicia with a handheld scanning device, wherein the operator can control the enablement of the aiming pattern in order to verify that the scanner is aiming at the proper barcode before initiating the decoding process.